If you want to replace the single trigger with a double set trigger you will probably have two problems.
The double set triggers often need a larger trigger guard to accommodate the second (rear) trigger.
Others mentioned that the lock used with a double set trigger needs a "fly" and your gun might not have one.
To find out if your lock has a fly in it, first make sure your gun is unloaded.
Then, pull the hammer back to full cock.
Place your thumb on the hammer spur and be ready to hold it in position and then, pull the trigger.
The hammer will start to jump downward but your thumb (or finger) should hold it just below the full cock notch engagement.
Now, slowly allow the hammer to move towards the fired position.
If your lock has a fly in it, the hammer will seem to pause just a little bit when it reaches the half cock position but, it will continue to fall to the completely "fired" position.
Sometimes the sear will hang up on the fly so, if it seems to stop at the half cock position, apply a little pressure to push it towards the fired position.
If it suddenly breaks loose and starts to continue to fall, your lock has a fly in it so you could install a double set trigger (if you resolve the trigger guard problem).
If the hammer comes firmly to a stop because the sear entered the half cock notch. your lock won't work with the most common type of double set triggers because it does not have a fly in it.
There is a double set trigger that will work with a lock that doesn't have a fly in it but most hunters don't like them.
That's because the front trigger will only fire the gun if the rear trigger is set first.
This "other type" of double set trigger will keep the hammer from being fully cocked unless the rear trigger is "set" first, before cocking.
The half cock notch also won't work unless the rear trigger is "set" before bringing up the hammer to the half cock position.
As I said, many hunters don't like walking around with a fully cocked set trigger that can try to fire with the brush of a twig.
Target shooters don't worry about this so they often like these special "Single Lever" set triggers.